1. Field of the Invention
The present invention is in the field of image processing, particularly in the field of image reconstruction, such as reconstructing an image from data acquired with a magnetic resonance apparatus.
2. Description of the Prior Art
Magnetic resonance tomography (MRT) is a modern imaging modality wherein a static, basic magnetic field aligns the nuclear spins of selected nuclei in an examination subject that were previously randomly oriented. Radiofrequency energy is irradiated into the examination subject, causing the spins to “tip” and emit magnetic resonance signals as they return to their equilibrium state. Using these magnetic resonance signals, slice exposures can be generated etc. Slice exposures can be generated of nearly every body part at any angle and in any direction. The data exist in digital form and can be processed into meaningful images by the use of computer systems. The average examination time is approximately 20 to 60 minutes. Due to the physical principle for acquiring the measurement data, the slice images must be processed into a three-dimensional representation, so it is necessary to process a large amount of digital data. This places high performance and storage demands on the processing components.
Imaging methods are used not only in the field of diagnostics but also are used to supervise or conduct interventional or surgical procedures, wherein the imaging can occur online (in real time). It is thereby necessary to achieve as optimal a performance as possible, both as to the acquisition system for the measurement data and as to the calculation process for the measurement data, in order to be able to keep the risks for the patient as minimal as possible. For example, MR-controlled procedures exist in the field of interventional radiology such as biopsies, interventions for liver tumors, treatment of osseous lesions, and percutaneous vertebral biopsies particularly in interventional radiology it is an indispensable requirement that an optimized image processing and imaging can be ensured in real time in order to be able to plan the precision of the procedure and in order to be able to ensure the highest patient safety.
Methods for efficiency improvement are known. The article “Efficiency visualization of large medical image Datasets on standard PC hardware”, Proceedings of the symposium on Data visualization, ACM International Conference Proceeding Series; Vol. 40, pages 135-140 from the year 2003 by Pekar, V. et al. discloses a hardware-based approach in order to be able to efficiently display medical image data. Here an algorithm is proposed that is applied to already-acquired medical image data and is intended to enable a more efficient visualization of the image data in that a memory caching strategy is modified. The algorithm disclosed therein deconstructs (dismantles) the data set such that it is adapted to the size of the cache. This is also achieved by a parallel processing. This article, however, does not disclose a suitable, interdependent nesting (interleaving) strategy for a combined acquisition and calculation process in which the later calculation process is separated such that an optimal result can be achieved with regard to the sequence of the data acquisition.
Moreover, U.S. Application Publication 2004/0223003 A1 discloses an image processing method and an associated image generator in which an overall image is deconstructed into image parts that are respectively processed in parallel-executed threads with rendering units and merging units being provided in the threads. The processing speed for display of an image data set in fact can be increased with the approach proposed in this publication, but there is no description of a combined acquisition and calculation process wherein the calculation process is structured so as to be optimal for the acquisition process, particularly the sequence of the acquired image data.
A basic factor of importance is the computer-controlled acquisition and processing of the image data. It is necessary to ensure that degradations or limitations due to the imaging do not occur. Furthermore, it is important to control the image data acquisition (via the modality of the magnetic resonance tomography apparatus in the example above), particularly the scan control, such that the image reconstruction and image evaluation based thereon can ensue in a time-optimized manner.
A magnetic resonance tomography system typically includes a basic field magnet that generates a static magnetic field in order to polarize the atomic nuclei in the body or body part to be examined. A transmitter for radio-frequency pulses and corresponding receivers are used for exciting the MR signal and the acquisition thereof. A system computer controls the measurement data acquisition and is used for the administration of measurement data as well, plus the further processing of the data or and for the reconstruction of images from the acquired measurement data. Since the further calculation of image data and the reconstruction of images are based on the acquisition of the respective measurement data, it is necessary for specific ranges of measurement data to be acquired in a temporally preliminary (advance) phase in order to later be processed for the reconstruction. This, however, would lead to unacceptable delays if the measurement process would have to be completely executed before the subsequent reconstruction can be started. A decisive point for the performance (quality) of such systems is the temporal meshing between the acquisition process and the subsequent calculation process.
A combined acquisition and calculation of measurement data are known, but these known solutions are based on a pipeline-like, serial processing of input data. The image data are acquired in a specific manner and in a specific order (i.e. in a specific measurement sequence). This measurement sequence, thus the order of the acquisition of the measurement data, typically can be configured by controlling the hardware of the MR scanner in a specific manner. The calculation process thus is disadvantageously not flexibly adaptable. In particular, conventionally it has not been possible to change the configuration of the calculation process. Previous systems are thus dependent on an explicit and additional synchronization between the reconstruction process and the acquisition process and/or on a predetermined temporal measurement order. The accuracy (and therewith the performance) of the overall system thus disadvantageously depends on an additional task, namely the explicit synchronization and/or the retention of the necessary measurement order. If this task can only be imperfectly executed, the result of the image reconstruction can likewise be imperfect or even unusable (from a qualitative and/or temporal point of view).
Moreover, there are multiple calculation processes (in particular reconstruction processes) that can be used in this context. It has proven to be disadvantageous that there is no uniform and/or no complete description of these calculation processes.
Therefore it has not been conventionally possible to adapt the calculation processes to the requirements of the acquisition process. By contrast, in specific situations the acquisition process (in particular the order of the measurement data acquisition) would have to be adapted to the requirements of the reconstruction process. This is only possible, however, in a very limited manner since (particularly in MR image data acquisition) there are a number of physical requirements that must be adhered to and that thus limit the configuration freedom. The possibilities for influencing and the interlocking of the two processes are therefore sub-optimal in the known systems.